Interesting. My guess is one of two things. I seem to recall Adila using boron in shafts a few years ago...increased breaking point allowing for some other interesting properties. But Mizzy doesn't do a lot of graphite irons so my next guess is boron nitride, one of the hardest substances known to mankind. That would allow for a very thin face without sacrificing trampoline. Boron wouldn't be a particularly good weight since it's actually not common at all and only something you would want to use as a small portion of a club.
Anyway, my money is on boron nitride faces. More than likely wrong, though.
Anyway, my money is on boron nitride faces. More than likely wrong, though.